The present invention relates to a balloon used for various kinds of balloon catheters, especially for a dilatation catheter used for expanding a stenotic lesion in a blood vessel, a catheter equipped with the balloon, and the method or manufacturing the balloon.
There are proposed some methods of manufacturing a balloon for a catheter balloon. Disclosed in Japanese Patent Provisional Publication gazette No. 26655/1988, for example, is a method of manufacturing a biaxially-drawn polymer balloon, in which a thin wall tubular parison is formed out of a drawable hemicrystalline polymer, the parison is stretched out in the direction of its length and then inflated radially at a temperature in the range from the second-order transition temperature to the first-order transition temperature, and the thus-drawn parison is cooled below the second-order transition temperature and deflated.
Another method of manufacturing a biaxially-drawn polymer balloon is proposed in Japanese Patent Provisional Publication gazette No. 183070/1988, in which the parison drawn by the same method is heated to a temperature above the drawing temperature while drawn to raise the crystallinity and then cooled below the second-order transition temperature.
The catheter balloon manufactured by the above conventional methods consists of a cylindrical portion of a substantially uniform diameter, tapered portions at the front and rear of the cylindrical portion, and thinner cylindrical connecting portions at the front and rear of the tapered portions.
The wall thickness of the catheter balloon made by the above methods is not uniform and the walls of both tapered portions are thicker than that of the cylindrical portion. More specifically the wall thicknesses b1 and b2 of the middle parts of the tapered portions are thicker than the thickness a of the cylindrical portion as shown in FIG. 4. Here the middle part of the tapered portions 3a and 3b means the vicinity of the middle point of their length along the axis of the balloon 1. Because of their thicker walls, the tapered portions wrinkle when the balloon is folded and the wrinkles are angular, protuberant and stiff. These wrinkles can hinder the smooth insertion of the balloon into a stenotic lesion in the blood vessel or hurt the inside surface of the blood vessel to cause thrombosis or stenosis.